1. Field of the Invention
This invention relates to a method of optically recording information on an information recording medium.
2. Description of the Related Art
Onto a recordable or rewritable optical disc such as a DVD-R (DVD-Recordable) or a DVD-RW (DVD-Rerecordable), information is recorded thereon by irradiating a laser beam on its recording surface. At the areas on the recording surface of the optical disc where the laser beam is irradiated, the property of the optical recording medium forming the optical disc is physically changed because of the increased temperature. This generates recording marks on the recording surface.
Therefore, if the laser beam is modulated by a pulse waveform (it is called “strategy”) corresponding to information to be recorded, and irradiated on the optical disc, recording marks having lengths corresponding to the information to be recorded can be formed on the optical disc.
As a strategy for recording the information on a rewritable optical disc such as a DVD-RW, there is well known a strategy including a top pulse and multi-pulses (they are also called “pulse train”) of the number corresponding to recording mark lengths. For instance, an example thereof is disclosed in Japanese Patent No. 2801510.
Recently, there is a demand of the strategy which is adapted to high-speed recording of more than 4-times higher speed, for the purpose of improvement of a recording speed. However, according to the strategy which utilizes the above-mentioned multi-pulse, ON/OFF switching of the pulse has to be executed within a time of 1T (“T” indicates a base clock period of a recording signal) because multi-pulse number is increased in 1T unit corresponding to the recording mark length. Therefore, if the base clock becomes higher speed in the high-speed recording and the time of 1T becomes shorter, it becomes difficult to obtain an accurate emitting waveform because the rounding portion of the multi-pulse waveform becomes larger by a transient response. Thus, a recording characteristic of the optical disc is easily affected by differences of characteristics of a laser light source and a driving circuit between recording apparatuses.
Also, since heating by the laser beam and cooling cannot be executed longer than a 1T time period in the multi-pulse period, the mark cannot be formed satisfactorily dependently on the characteristic of the optical disc, and the recording characteristic sometimes becomes worse, like the decrease of a signal modulating degree. The present invention has been achieved in order to solve the above problems.